The present invention relates generally to satellite communication systems, and more particularly to a method and system for detecting signal lock between a satellite receiver and a satellite in a digital DBS system.
Generally, in modem digital satellite communication systems a ground-based transmitter transmits a forward-error-coded uplink signal to a satellite positioned in geosynchronous orbit. The satellite in turn relays the signal back to a ground-based receiver antenna in a separate location. Direct broadcast satellite ("DBS") systems allow households to receive audio, data, and video directly from the DBS satellite. Each household subscribing to the system receives the broadcast signals through a receiver unit and a satellite dish receiver antenna.
The typical consumer DBS system consists of a satellite receiver antenna which includes an e.g. 18-inch parabolic dish and low noise block ("LNB"), and a receiver unit which may include an integrated receiver decoder module, or "IRD". The receiver antenna is typically mounted outside the house, and cables are provided to link the LNB to the indoor IRD and associated equipment (e.g. video display).
Several factors can degrade received DBS signals. For example, the satellite receiver antenna can accumulate snow, ice, leaves, or other debris unseen by the user. Remote blockage may also develop, such as shadowing foliage (e.g. trees). This accumulation or other shadowing obstruction can degrade the received signal strength enough to interrupt IRD operation. Furthermore, due to the significant amount of forward error correction used, the DBS picture or data quality may not suffer any noticeable decrease although signal strength is continuously degrading. When signal strength falls below a certain minimum, the signal can be completely lost without warning.
Other sources of DBS signal degradation include antenna tracking errors in mobile installations, such as ships, trains, or automobiles, each of which require constant adjustments to the receiver antenna's orientation. As with fixed DBS systems, the signal degradation in a mobile DBS installation can result in complete loss of signal lock without warning.
Therefore, there is a need for an inexpensive and simple method and system for automatically detecting signal degradation and for warning the user when a DBS signal is degrading, to provide an incipient signal loss warning or reaction. There is a particular need for such a method and system which may be added to existing satellite receiving equipment without modification, e.g. as an "add-on" device.